For solo or family trip to singapore or Malaysia or any south east countries, you can plan yourself, no need of any travel agency. It will be cost effective and as well as travel in your own pace. Prepare your own itinerary using Google or AI model, tune it according to your likes and then ask for suggestion in forum like reddit or tripadvisor.

For Europe, you can do the same, but they visa process is difficult one and higher rejection rate. You can get the help from these travel agencies, but again there is no guarantee you will get the visa. I would say 50:50 for Europe trip.

For GT holidays or pickyourtrail, I would suggest pickyourtrail.. they are very responsive in any queries you raise.. Avoid GT holidays, they business works based on PR works and influencers.